EP3453679B1

EP3453679B1 - Method for producing high-purity tungsten pentachloride

Info

Publication number: EP3453679B1
Application number: EP17877988.0A
Authority: EP
Inventors: Hideyuki Takahashi
Original assignee: JX Nippon Mining and Metals Corp
Current assignee: JX Nippon Mining and Metals Corp
Priority date: 2016-12-05
Filing date: 2017-10-06
Publication date: 2023-04-05
Anticipated expiration: 2037-10-06
Also published as: EP3453679A4; JP6517375B2; TW201831407A; US20190233301A1; TWI725247B; KR102254275B1; WO2018105220A1; JPWO2018105220A1; EP3453679A1; KR20190017941A; US11427479B2

Description

TECHNICAL FIELD

The present disclosure relates to high purity tungsten pentachloride and a production method thereof suitable for electronic devices such as semiconductor devices and a production process thereof, functional chemical catalysts, and compound synthetic raw materials.

BACKGROUND ART

Since metallic tungsten (W) has electrically low resistivity (roughly 5 to 6 µΩ▪cm) and has a characteristic of little electro migration, and is also relatively stable chemically, tungsten has been often used conventionally as "contact plugs", "interconnection", or "diffusion barrier layers under the interconnection" of functional electronic devices such as semiconductor components. A compound of tungsten is also frequently used for the diffusion barrier layer.
The formation of a layer formed from this kind of metallic tungsten or a compound thereof has often been performed conventionally based on Chemical Vapor Deposition (CVD) which uses a precursor compound of a gas phase containing a tungsten element. Moreover, pursuant to the higher integration and higher densification of devices in recent years, the narrowing of pitches of the wire forming part and the stretching of deep parts of the contact plug are also advancing, and it tends to form the tungsten layer on a concave part with a high aspect ratio. In order to uniformly form a tungsten layer inclusive of the side wall of the concave part with a high aspect ratio, also adopted is a technique of foremost uniformly forming a W seed layer in the concave part via Atomic Layer Deposition (ALD), and subsequently forming a thick tungsten layer via CVD described above or via plating.
Upon forming a layer formed from tungsten or a compound thereof via CVD or ALD, tungsten hexafluoride (WF₆) has been often used conventionally as the precursor compound (refer to Patent Document 1 and the like). Nevertheless, with processes using WF₆, there are problems in that the fluorine (F) remaining in trace amounts in the film causes the electro migration of the apparatus, and a part of the apparatus becomes corroded by the highly corrosive fluorine gas (F₂) that is generated due to the decomposition of the precursor.
As a means for resolving the foregoing problems, the use of tungsten chloride, which is a compound of chlorine (CI) having a lower reactivity than fluorine, and tungsten, is being considered. Tungsten chloride has a plurality of different compound forms such as tungsten hexachloride (tungsten chloride (VI): WCl₆), tungsten pentachloride (tungsten chloride (V): WCl₅), tungsten tetrachloride (tungsten chloride (IV): WCl₄), and tungsten dichloride (tungsten chloride (II): WCl₂) depending on the difference in the valence of tungsten.
Among the above, WCl₅ has a high vapor pressure in comparison to WCl₆ and the like, yields superior film thickness uniformity (step coverage) when used as a precursor upon depositing a film on a high aspect ratio part, is also characterized in that etching of the substrate does not occur easily (refer to Patent Document 2 and the like), and is a compound material that is particularly suitable as a precursor material for use in CVD or ALD.
Moreover, WCl₅ is also characterized in that it is soluble in many solvents among the tungsten chlorides, and is extremely useful as a catalyst upon synthesizing functional chemicals and as a raw material upon synthesizing other tungsten compounds. As described above, WCl₅ as a pentavalent tungsten chloride is a compound that is becoming more important for use as electronic materials, use as chemical synthetic catalysts, and use as compound raw materials, it goes without saying that it would be desirable to efficiently obtain a high purity compound in all of the foregoing uses.
Conventionally, WCl₅ is often obtained by subjecting WCl₆ to hydrogen reduction at a moderate level as disclosed in Non-Patent Document 1. Moreover, Non-Patent Document 2 discloses a means for obtaining WCl₅ by using Bi, Hg, Sb or the like as the reducing agent and reducing WCl₆ under reduced pressure. According to this means, it is possible to perform the reduction in a highly efficient manner, and, in addition to being able to reduce the reaction time, it is expected that the generation of products other than WCl₅ can be considerably suppressed based on uniform reduction.

CITATION LIST

Patent Documents

[Patent Document 1] Japanese Unexamined Patent Application Publication No. 2015-193908
[Patent Document 2] Japanese Unexamined Patent Application Publication No. 2015-221940

Non-Patent Documents

[Non-Patent Document 1] Takashi Takuma, Seiichiro Kawakubo, Journal of the Chemical Society of Japan, 1972, No. 5, pp. 865-873
[Non-Patent Document 2] V. Kolesnichenko et al., Inorg. Chem., Vol. 37, No. 13 (1998), pp. 3257-3262

EP 3 409 647 is a document citeable under Art. 54(3) EPC and discloses high purity tungsten pentachloride and a method for synthesizing the same.

SUMMARY OF INVENTION

TECHNICAL PROBLEM

Nevertheless, with the conventional hydrogen reduction method, there are problems in that the reduction efficiency is low and much reaction time is required, and it is difficult to control the hydrogen flow rate and the temperature. Moreover, in case that the system is scaled up for mass production, there are problems in that nonuniformity of the degree of reduction will partially arise, and residue of WCl₆, and products such as WCl₄, WCl₂, and W other than the intended WCl₅, are generated in an amount exceeding the tolerated level.
Moreover, with the means of using Bi, Hg, Sb or the like as the reducing agent and reducing WCl₆ under reduced pressure, the reaction product of the reducing agent and WCl₆ becomes sublimated during reduction unless the process and conditions are properly set, and there is a problem in that the reaction stops midway and a large amount of the reducing agent will remain in the raw material. Furthermore, the yield of WCl₅ (raw material yield rate) that is obtained relative to the used WCl₆ raw material will only be 50% or less, and there is a problem in that the production yield in light of the purity, the yield and reaction time of the ultimately obtained WCl5 are not necessarily at the level that is expected in comparison to conventional technologies.

SOLUTION TO PROBLEM

As a result of intense study, the present inventors discovered that high purity WCl₅ can be obtained at a high yield and in a highly efficient manner by controlling the pressure and temperature range in a method of obtaining WCl₅ by using a reducing agent and reducing WCl₆ while maintaining a state in which a chloride of a reducing agent and W becomes a liquid phase, subsequently performing reduction, and thereafter additionally performing reduced-pressure distillation and sublimation purification, and thereby completed the present invention.
Based on the foregoing discovery, the present invention provides a method of producing tungsten pentachloride as claimed.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, it is possible to obtain WCl₅, which can be used as a material for electronic devices such as semiconductor components, chemical synthetic catalysts and compound raw materials, as a high purity product which not only has a low impurity element content but which also has a low content of tungsten chloride having a different valence such as WCl₆ and WCl₄ other than WCl₅. Moreover, since it is possible to obtain this kind of high purity WCl₅ at a higher yield and higher efficiency in comparison to conventional technologies, it is possible to improve the production yield and reduce the production cost.

BRIEF DESCRIPTION OF DRAWINGS

[Fig. 1] Fig. 1 is a diagram showing configuration examples of apparatuses for working the present invention.

DESCRIPTION OF EMBODIMENTS

WCl₅ of the present disclosure is characterized in that it is a high purity product in which the total content of metal impurities excluding Sb, Ti, and As is less than 10 wtppm. These metal impurities also get mixed in as impurities in the wiring material when forming the wiring of electronic devices, and are preferably eliminated because they cause the increase of resistivity, generation of electro migration, and diffusion into the device, which leads to the deterioration in the performance and life of the device, and in certain cases leads to the malfunction of the device.
The content of metal impurities excluding Sb, Ti, and As described above is preferably less than 8 wtppm, and more preferably less than 3 wtppm. Among the above, the content of Mo is preferably 2 wtppm or less, and more preferably 1.5 wtppm or less. Note that "wtppm" which represents the unit of the content of trace elements indicates the value of the weight basis.
Here, the metal impurities refer to the respective elements of Ag, Na, Cd, Co, Fe, In, Mn, Ni, Pb, Zn, Cu, Cr, Ti, TI, Li, Be, Mg, Al, K, Ga, Ge, As, Sr, Sn, Sb, Ba, Mo, U, and Th, and the contents thereof basically refer to the values analyzed based on Inductively Coupled Plasma Mass Spectrometry (ICP-MS). With regard to elements in which the value detected based on the foregoing analysis is less than the detection lower limit, it is deemed that the content of those elements is zero and such elements are not substantially included.
Among the foregoing impurities elements, the respective elements of Sb, Ti, and As are elements that may be used as a reducing agent upon producing WCl₅ as described later, and when these elements are used as a reducing agent, they will indicate a highly significant content in comparison to other metal elements. In this way, when a significantly high content is detected beyond the detection lower limit, the accurate content is analyzed once again based on Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES), and this will be used as the content of Sb, Ti, and As.
Moreover, WCl₅ of the present disclosure may contain a total content of one or more elements selected from Sb, Ti, and As within a range of 0.01 wtppm or more and less than 200000 wtppm. Among the above, when a moderate amount of Sb or As is included, this WCl5 can form element containing V group (5B group) element acting as a dopant contributing to control of the electrical properties depending on the mode of use, and, when a moderate amount of Ti is included, it is possible to yield the effect of improving the barrier properties and adhesiveness when used for the deposition of a diffusion barrier layer in semiconductor apparatuses.
From the foregoing perspective, the content of Sb, Ti, and As as a dopant is preferably 0.01 wtppm or more when used as a low concentration dopant, and may also be 0.05 wtppm or more or 0.1 wtppm or more depending on the mode. When used as a low concentration dopant, the content of these elements is preferably less than 1 wtppm, and may also be 0.8 wtppm or less or 0.5 wtppm or less depending on the mode. When used as a high concentration dopant, the content of these elements is preferably 500 wtppm or more, and may also be 1000 wtppm or more, 3000 wtppm or more, or 5000 wtppm or more depending on the mode. When used as a high concentration dopant, the content of these elements is preferably 200000 wtppm or less, and may also be 150000 wtppm or less or 100000 wtppm or less depending on the mode.
More specifically, the content of Sb is preferably 500 wtppm or more, and may also be 1000 wtppm or more, 3000 wtppm or more, or 5000 wtppm or more depending on the mode. Moreover, when the amount of Sb is excessively great, since it may not be possible to sufficiently exhibit the properties of the intended dopant film, the amount of Sb may be 20000 wtppm or less, and may also be 15000 wtppm or less, 10000 wtppm or less, or 8000 wtppm or less depending on the mode.
Similarly, the content of Ti may be 0.1 wtppm or more, 0.4 wtppm or more, or 0.8 wtppm or more depending on the mode, and the upper limit may be 100000 wtppm or less, and may also be 50000 wtppm or less, or 35000 wtppm or less depending on the mode, and, when a low Ti content is preferable, the content of Ti may be 20 wtppm or less, 10 wtppm or less, and even 1 wtppm or less.
The content of As may be 1000 wtppm or more, 5000 wtppm or more, or 10000 wtppm or more depending on the mode, and the upper limit may be 50000 wtppm or less, and may also be 20000 wtppm or less, or 14000 wtppm or less depending on the mode.
In the present disclosure, while tungsten chlorides having a different valence such as WCl₆, WCl₂, and WCl₄ other than WCl₆ and W-O-CI-based acid chloride are compound impurities that are not detected as the element impurities described above, it is also preferable to decrease these compound impurities having a different valence. WCl₅ of the present disclosure is characterized in that the total content of WCl₆, WCl₂, WCl₄, and W-O-CI-based acid chloride is 5 wt% or less. Note that, in the present disclosure, the content of WCl₆, WCl₂, WCl₄, and W-O-CI-based acid chloride is a value obtained by quantifying the weight variation via measurement based on thermogravimetry (TG).
The method of using one or more types of elements selected from Sb, Ti, and As as a reducing agent and reducing WCl₆ under specific conditions, and subsequently performing reduced-pressure distillation and sublimation purification, is adopted, since it is possible to obtain high purity WCl₅ at a high yield and in a highly efficient manner.
With the method described above, foremost, a process of uniformly mixing one or more types of reducing agents selected from Sb, Ti, and As and WCl₆ at a molar ratio of 1.0:2.0 to 1.0:5.0 in an inert atmosphere to obtain a mixture is performed. When the amount of the reducing agent is great in excess of 1.0:2.0, a large amount of the reducing agent will remain, and much time will be required for the subsequent reduced-pressure distillation and sublimation purification. When the amount of WCl₆ is great in excess of 1.0:5.0, this may lead to a large amount of unreduced WCl₆ remaining in the product. The mixing ratio of the reducing agent and WCl₆ is more preferably 1.0:3.0 to 1.0:4.0, and a molar ratio that matches the metal valence of the product (1.0:3.0 in the case of Sb and As, and 1.0:4.0 in the case of Ti) is the most preferable.
In the process described above, it is possible to use one or more elements selected from Sb, Ti, and As which yield the effect of reducing WCl₆ as a reducing agent. Moreover, with the reducing agent and WCl₆ as the raw material to be mixed with the reducing agent, high purity materials are preferably used for both, and, for instance, materials having a purity of 4N or higher may be preferably used. As a result of using a high purity raw material, it is possible to lower the melting point and promote the reaction.
There is no particular limitation in the method of mixing the reducing agent and WCl₆ as long as the method is able to uniformly mix to generate a reduction reaction in the proper amount sufficiently; the mixing may be performed using a ball mill, a jet mill, an agitation mixer, a mortar or the like. Here, when performing the mixing, it is important to prevent the oxidation of the raw material and the reducing agent, and perform the mixing in an inert atmosphere in order to prevent the inclusion of oxygen impurities. As the inert atmosphere, argon (Ar), helium (He) and other rare gases, nitrogen (N₂) and the like which do not react with the raw material and the reducing agent in a normal temperature may be used.
The mixture obtained by uniformly mixing the reducing agent and the raw material is subject to the following reduction process, and at this stage the grain size of the raw material is preferably at least 200 µm or less, and the grain size of the overall raw material mixture including the reducing agent is preferably 200 µm or less. As a result of reducing the grain size of the raw material as described above, it is possible to increase the reactivity and efficiently promote the reaction, and thereby prevent the residue of unreduced products. In order to cause the grain size of the raw material, or the grain size of the mixture of the reducing agent and the raw material, to fall within the foregoing range, in addition to preparing materials having a grain size of 200 µm or less at the stage before the mixture, the mixing performed by the various mills and mortar described above may also double as the pulverization of such materials. The grain size is preferably 200 µm or less, and may also be 150 µm or less depending on the mode. Note that the term "grain size" as used in the present disclosure refers to the diameter D90 which becomes 90% of the overall mass in the grain size distribution.
Next, the mixture of the reducing agent and the raw material obtained from the foregoing process is heated and reduced to obtain a reduced product. In this process, while the reducing agent reacts with the chlorine contained in the raw material and forms a chloride of the reducing agent element, what is important here is that the foregoing reduction process is performed while controlling and maintaining the pressure and temperature range in which the chloride of the reducing agent element will be a liquid phase. As a result of performing the reduction process under the foregoing conditions, it is possible to prevent the chloride of the reducing agent element, which is formed based on the reaction, from excessively becoming sublimated and causing the reaction to stop midway, and consequently prevent the reducing agent from remaining in a large amount, and considerably deteriorating the yield of WCl₅.
The scope of rough standard of pressure and temperature during reduction differs depending on the type of reducing agent. When Sb is used as the reducing agent, while SbCl₃ as the chloride of Sb can maintain a liquid phase state by controlling the pressure to be 0.1 to 2 MPa and the temperature to be 70 to 100°C, the temperature is preferably 72 to 80°C to stably promote the reduction reaction. Similarly, when Ti is used as the reducing agent, the chloride of the reducing agent element preferably reduces maintaining a liquid phase state by controlling the pressure to be 0.1 to 2 MPa and temperature to be 100 to 130°C, and when As is used as the reducing agent, the chloride of the reducing agent element preferably reduces maintaining a liquid phase state by controlling the pressure to be 0.1 to 100 MPa and temperature to be -16 to 60°C.
By performing the reduction reaction within the foregoing range, it is possible to stop the react at the point in time that WCl₅ is synthesized prior to the synthesis of a more stable WCl₄. The reduction reaction is preferably performed in a dry nitrogen flow atmosphere having a moisture content of 10 wtppm or less. Moreover, it depends on the amount of the raw material and the amount of the reaction product, the foregoing reduction reaction is preferably performed for 1 hour or longer for sufficient reaction, and may be performed for 10 hours or longer. Since the prolonged performance of the reduction reaction beyond necessity is undesirable in terms of production efficiency, the reduction reaction should be stopped at 100 hours, or at 50 hours depending on the mode.
Next, the reduced product obtained with the foregoing process is subject to reduced-pressure distillation to obtain a reduced-pressure distilled product. In this process, the impurities contained in the reduced product are distilled under a reduced pressure of 100 Pa or less, preferably 50 Pa or less, to mainly eliminate impurities such as SbCl₃, WOCl₄, and WO₂Cl₂ having a lower sublimation point than the target WCl₅. The heating temperature during distillation is set to a range of 90 to 130°C, and distillation is performed for 1 hour or longer, preferably for 10 to 100 hours.
Furthermore, the reduced-pressure distilled product obtained with the foregoing process is subject to sublimation purification to obtain a high purity WCl₅ product. In this process, the area where the reduced-pressure distilled product is to be sublimated is heated in a temperature range of 130 to 170°C and the area where WCl₅ is to be reprecipitated is set to a temperature range of 70 to 120°C in an inert atmosphere of 100 Pa or less, preferably 50 Pa or less, to recover high purity WCl₅. Sublimation purification is performed for 1 hour or longer, preferably for 10 to 100 hours. Consequently, high purity WCl₅ is generated at the precipitated part based on sublimation reprecipitation on the one hand, and impurities such as WCl₄ and oxides of the reducing agent element having a higher sublimation point than WCl₅ will remain at the heated part on the other hand. Here, the recovered WCl₅ may repeatedly be subject to similar sublimation purification, and it is thereby possible to obtain high purity WCl₅.
The configuration of apparatuses that are suitable for performing the foregoing processes is illustrated in Fig. 1. In all modes of Fig. 1(a) to Fig. 1(c), a processing object 101 is heated within a heating vessel 102. In the reduction process, the processing object 101 is a mixture of WCl₆ and a reducing agent, and heated in the heating vessel so that the chloride of the reducing agent becomes a liquid phase state. In the subsequent reduced-pressure distillation process, pressure is reduced in the heating vessel 102, and the processing object 101, which became a reduced product in the reduction process, is heated, but a sublimated product having a lower sublimation point than the generated WCl₅ is cooled and collected by a cold trap 103. Subsequently, in the modes of Fig. 1(a) and Fig. 1(b), the cold trap 103 is replaced and the precipitation temperature is set, and the sublimation temperature of the heating vessel 102 is set and sublimation purification is performed. Refined WCl₅ thereby becomes precipitated in the cold trap 103.
Meanwhile, in the mode of Fig. 1(c), the heating vessel 102 is configured as a furnace in which the temperature gradient can be set in the horizontal axis direction thereof, and, by setting a sublimated part 111 to the sublimation temperature and setting a precipitated part 112 to the precipitation temperature, respectively, sublimation purification can be performed in the heating vessel 102. Note that the foregoing apparatus configurations merely illustrate examples that can be applied upon actually working the present disclosure, and it goes without saying that configurations modified as needed and other arbitrary configurations may also be adopted.
According to the method of the present invention, in addition to being able to improve the yield of WCl₅, which had stopped at 50% or less in conventional technologies, to roughly 65 to 80%, in the reduction process the chloride of the reducing agent element will not cause the reaction to stop because it will not become sublimated, and it is thereby possible to efficiently obtain high purity WCl₅. Note that the expression "yield of WCl₅" as used in the present invention refers to the numerical value which expresses, as a percentage, the mass of WCl₅ actually recovered from precipitates based on sublimation purification relative to the mass of 3WCl₅ or 4WCl₅ which is theoretically anticipated based on the reaction of following Formulas (1) to (3) concerning WCl₆ (raw material) and the reducing agent, i.e. ((actually recovered mass of WCl₅ / theoretically recovered mass of WCl₅) × 100(%)).

3WCl₆ + Sb → 3WCl₅ + SbCl₃ (1)

4WCl₆ + Ti → 4WCl₅ + TiCl₄ (2)

3WCl₆ + As → 3WCl₆ + AsCl₃ (3)

Examples

The present invention is now explained in detail with reference to the Examples and Comparative Examples. Descriptions of the ensuing Examples and Comparative Examples are merely specific examples for facilitating the understanding of the technical contents of the present invention, and the technical scope of the present invention is not limited by such specific examples.

(Example 1)

WCl₆ having a purity of 4N and Sb having a purity of 5N as a reducing agent were uniformly mixed with a mortar in a nitrogen atmosphere to achieve a total mass of 1 kg at a molar ratio of 3:1. Next, the obtained mixture was placed in a vacuum vessel and heated at 150°C for 24 hours to reduce WCl₆ while maintaining the ambient pressure in the vessel to be an atmospheric pressure (approximately 0.1 MPa). During this reduction operation based on heating, SbCl₃, chloride of Sb as the reducing agent, was subject to the condition of maintaining a liquid phase state.
Subsequently, impurities were eliminated by subjecting the reduced product obtained with the foregoing reduction operation to reduced-pressure distillation through sublimation by being heated at 100°C for 24 hours while maintaining the ambient pressure in the vacuum vessel at 50 Pa. Furthermore, the obtained reduced-pressure distilled product was sublimated by being placed at a heated part having an atmospheric pressure of 50 Pa and being heated at 150°C, and sublimation purification was consequently performed by precipitating the product at a precipitated part of 90°C. The sublimation purification time was 24 hours. Subsequently, the obtained WCl₅ was recovered in a nitrogen atmosphere and sealed in an ampule.

Results of performing trace element analysis to the recovered WCl₅ are shown in Table 1. As impurities excluding Sb that was used as the reducing agent, Fe and Mo were detected in excess of the detection lower limit, the total content thereof was 9.1 wtppm. Moreover, the content of Sb was 6000 wtppm. Furthermore, as a result of performing a quantitative analysis regarding the contents of WCl₂, WCl₄, WCl₆, and W-O-CI-based acid chloride as compound impurities based on the TG method, the contents were respectively 0 wt%, 0 wt%, 1 wt%, and 3 wt%, and the total content was 4 wt%. In addition, a value of 78% was obtained as the yield of WCl₅ in this Example, and the achievement of a high yield was possible by using Sb as the reducing agent.

[Table 1]

		Example 1	Example 2	Example 3	Example 4	Example 5	Example 6	Example 7	Comparative Example 1	Comparative Example 2	Comparative Example 3	Comparative Example 4	Comparative Example 5	Comparative Example 6
	Ag	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	-	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1
	Na	< 1	< 1	< 1	< 1	< 1	< 1	< 1	-	< 1	3.8	3.5	4.1	2.5
	Cd	< 1	< 1	< 1	< 1	< 1	< 1	< 1	-	< 1	< 1	< 1	< 1	< 1
	Co	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	-	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1
	Fe	1.8	< 1	< 1	2.6	< 1	< 1	< 1	-	5.9	8.1	6.5	7.8	2.3
	In	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	-	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1
	Mn	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	-	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1
	Ni	< 1	< 1	< 1	< 1	< 1	< 1	< 1	-	< 1	< 1	< 1	< 1	< 1
	Pb	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	-	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1
	Zn	< 1	< 1	< 1	< 1	< 1	< 1	< 1	-	< 1	< 1	< 1	< 1	< 1
	Cu	< 1	< 1	< 1	< 1	< 1	< 1	< 1	-	< 1	< 1	< 1	< 1	< 1
	Cr	< 1	< 1	< 1	< 1	< 1	< 1	< 1	-	< 1	< 1	< 1	< 1	< 1
	Ti	< 1	0.9	32000	< 1	< 1	2900	0.2	-	< 1	< 1	< 1	31000	11000
	Ti	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	-	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1
Metal Impurity (wtppm)	Li	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	-	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1
	Be	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	-	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1
	Mg	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	-	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1
	Al	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	-	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1
	K	6	2	2	4	5	2	2	-	12	24	13	23	18
	Ga	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	-	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1
	Ge	< 0.2	< 0.2	< 0.2	< 0.2	< 0.2	< 0.2	< 0.2	-	< 0.2	< 0.2	< 0.2	< 0.2	< 0.2
	As	< 0.5	< 0.5	< 0.5	12000	< 0.5	< 0.5	< 0.5	-	< 0.5	< 0.5	< 0.5	< 0.5	< 0.5
	Sr	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	-	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1
	Sn	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	-	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1
	Sb	6000	< 0.1	< 0.1	< 0.1	7000	< 0.1	< 0.1	-	< 0.1	29000	19000	< 0.1	< 0.1
	Ba	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	-	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1
	Mo	1.3	0.5	0.5	1.2	1.4	1.5	0.5	-	2.1	1.9	1.2	1.9	1.8
	U	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	-	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1
	Th	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	-	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1
	Total Metal Content ^(*)	9.1	2.5	2.5	7.8	6.4	3.5	2.5	-	20.0	37.8	24.2	36.8	24.6
Ratio of Metal in Collected Sublimates (wt%)	WCl₂	0	0	0	0	0	0	0	-	0	-	0	-	0
	WCl₄	0	0	0	0	0	0	0	-	0	-	0	-	0
	WCl₅	96	99	99	96	20	95	62	-	81	-	80	-	85
	WCl₆	1	0	0	1	70	1	30	-	18	-	10	-	8
	W-O-Cl	3	1	1	3	10	4	8	-	4	-	10	-	7
	WCl₅ (9)	780	660	650	690	120	190	80	-	30	-	340	-	580
	Yield (%)	78	66	65	69	12	19	8	-	3	-	34	-	58

(*: Excluding elements Sb, Ti and As used as reducing agents

(Example 2)

WCl₆ having a purity of 4N and Ti having a purity of 5N as a reducing agent were uniformly mixed with a mortar in a nitrogen atmosphere to achieve a total mass of 1 kg at a molar ratio of 4:1. Next, the obtained mixture was placed in a vacuum vessel and heated at 130°C for 24 hours to reduce WCl₆ while maintaining the ambient pressure in the vessel to be an atmospheric pressure (approximately 0.1 MPa). During this reduction operation based on heating, TiCl_4, which is chloride of Ti as the reducing agent, was subject to the condition of maintaining a liquid phase state. Subsequently, the reduced product obtained with the foregoing reduction operation was subject to reduced-pressure distillation, and the thus obtained reduced-pressure distilled product was additionally subject to sublimation purification. The conditions of reduced-pressure distillation and sublimation purification were the same as Example 1. Subsequently, the obtained WCl₅ was recovered in a nitrogen atmosphere and sealed in an ampule.
Results of performing trace element analysis to the recovered WCl₅ are shown in Table 1. As impurities excluding Ti that was used as the reducing agent, K and Mo were detected in excess of the detection lower limit, the total content thereof was slightly 2.5 wtppm. Moreover, it was possible to suppress the content of Ti to a trace amount of 0.9 wtppm. Furthermore, as a result of performing a quantitative analysis regarding the contents of WCl₂, WCl₄, WCl₆, and W-O-CI-based acid chloride as compound impurities based on the TG method, the contents were respectively 0 wt%, 0 wt%, 0 wt%, and 1 wt%, and it was possible to effectively reduce the total impurity content by using a moderate amount of Ti as the reducing agent. In addition, a value of 66% was obtained as the yield of WCl₅ in this Example.

(Example 3)

WCl₆ having a purity of 4N and Ti having a purity of 5N as a reducing agent were uniformly mixed with a mortar in a nitrogen atmosphere to achieve a total mass of 1 kg at a molar ratio of 3:1 in which Ti becomes surplus. Next, the obtained mixture was placed in a vacuum vessel and heated at 130°C for 24 hours to reduce WCl₆ while maintaining the ambient pressure in the vessel to be an atmospheric pressure (approximately 0.1 MPa). During this reduction operation based on heating, TiCl_4, which is chloride of Ti as the reducing agent, was subject to the condition of maintaining a liquid phase state. Subsequently, the reduced product obtained with the foregoing reduction operation was subject to reduced-pressure distillation, and the thus obtained reduced-pressure distilled product was additionally subject to sublimation purification. The conditions of reduced-pressure distillation and sublimation purification were the same as Example 1. Subsequently, the obtained WCl₅ was recovered in a nitrogen atmosphere and sealed in an ampule.
Results of performing trace element analysis to the recovered WCl₅ are shown in Table 1. As impurities excluding Ti that was used as the reducing agent, K and Mo were detected in excess of the detection lower limit, the total content thereof was slightly 2.5 wtppm as with Example 2. Nevertheless, in this Example in which Ti as the reducing agent becomes surplus in comparison to Example 2, residue of Ti in an amount of 32000 wtppm was acknowledged. Furthermore, as a result of performing a quantitative analysis regarding the contents of WCl₂, WCl₄, WCl₆, and W-O-CI-based acid chloride as compound impurities based on the TG method, the contents were respectively 0 wt%, 0 wt%, 0 wt%, and 1 wt%, and it was possible to effectively reduce metal impurities and compound impurities other than the reducing agent even under a molar ratio condition in which the reducing agent becomes surplus. In addition, a value of 65% was obtained as the yield of WCl₅ in this Example.

(Example 4)

WCl₆ having a purity of 4N and As having a purity of 5N as a reducing agent were uniformly mixed with a mortar in a nitrogen atmosphere to achieve a total mass of 1 kg at a molar ratio of 3:1. Next, the obtained mixture was placed in a vacuum vessel and heated at 120°C for 24 hours to reduce WCl₆ while maintaining the ambient pressure in the vessel to be an atmospheric pressure (approximately 0.1 MPa). During this reduction operation based on heating, AsCl₃, which is chloride of As as the reducing agent, was subject to the condition of maintaining a liquid phase state. Subsequently, the reduced product obtained with the foregoing reduction operation was subject to reduced-pressure distillation, and the thus obtained reduced-pressure distilled product was additionally subject to sublimation purification. The conditions of reduced-pressure distillation and sublimation purification were the same as Example 1. Subsequently, the obtained WCl₅ was recovered in a nitrogen atmosphere and sealed in an ampule.
Results of performing trace element analysis to the recovered WCl₅ are shown in Table 1. As impurities excluding As that was used as the reducing agent, Fe, K and Mo were detected in excess of the detection lower limit, the total content thereof was 7.8 wtppm. Moreover, the content of As was 12000 wtppm. Furthermore, as a result of performing a quantitative analysis regarding the contents of WCl₂, WCl₄, WCl₆, and W-O-CI-based acid chloride as compound impurities based on the TG method, the contents were respectively 0 wt%, 0 wt%, 1 wt%, and 3 wt%, and the total content was 4 wt%. In addition, a value of 69% was obtained as the yield of WCl₅ in this Example.

(Example 5)

This example is not in accordance with the claimed invention. WCl₆ having a purity of 4N and Sb having a purity of 5N as a reducing agent were uniformly mixed with a mortar in a nitrogen atmosphere to achieve a total mass of 1 kg at a molar ratio of 3:1. Next, the obtained mixture was placed in a vacuum vessel and heated at 60°C for 24 hours to reduce WCl₆ while maintaining the ambient pressure in the vessel to be an atmospheric pressure (approximately 0.1 MPa). In this Example, since the temperature during this reduction operation was low, SbCl₃, which is chloride of Sb as the reducing agent, was in a solid phase state without becoming a liquid phase state. Subsequently, the reduced product obtained with the foregoing reduction operation was subject to reduced-pressure distillation, and the thus obtained reduced-pressure distilled product was additionally subject to sublimation purification. The conditions of reduced-pressure distillation and sublimation purification were the same as Example 1. Subsequently, the obtained WCl₅ was recovered in a nitrogen atmosphere and sealed in an ampule.
Results of performing trace element analysis to the recovered WCl₅ are shown in Table 1. As impurities excluding Sb that was used as the reducing agent, K and Mo were detected in excess of the detection lower limit, the total content thereof was 6.4 wtppm. Nevertheless, in this Example in which the temperature during reduction is of a lower condition than Example 1, residue of Sb in an amount of 7000 wtppm was acknowledged. Furthermore, as a result of performing a quantitative analysis regarding the contents of WCl₂, WCl₄, WCl₆, and W-O-CI-based acid chloride as compound impurities based on the TG method, the contents were respectively 0 wt%, 0 wt%, 70 wt%, and 10 wt%, and the yield of WCl₅ was 12%. When the chloride of the reducing agent remains in a solid phase, while this is effective in reducing metal impurities other than the reducing agent, a large amount of WCl₆ will remain, and the yield will deteriorate considerably.

(Example 6)

This example is not in accordance with the claimed invention. WCl₆ having a purity of 4N and Ti having a purity of 5N as a reducing agent were uniformly mixed with a mortar in a nitrogen atmosphere to achieve a total mass of 1 kg at a molar ratio of 4:1. Next, the obtained mixture was placed in a vacuum vessel and heated at 160°C for 24 hours to reduce WCl₆ while maintaining the ambient pressure in the vessel to be an atmospheric pressure (approximately 0.1 MPa). In this Example, since the temperature during this reduction operation was excessively high, TiCl_4, which is chloride of Ti as the reducing agent, became a gas phase state. Subsequently, the reduced product obtained with the foregoing reduction operation was subject to reduced-pressure distillation, and the thus obtained reduced-pressure distilled product was additionally subject to sublimation purification. The conditions of reduced-pressure distillation and sublimation purification were the same as Example 1. Subsequently, the obtained WCl₅ was recovered in a nitrogen atmosphere and sealed in an ampule.
Results of performing trace element analysis to the recovered WCl₅ are shown in Table 1. As impurities excluding Ti that was used as the reducing agent, K and Mo were detected in excess of the detection lower limit, the total content thereof was 3.5 wtppm. Furthermore, as a result of performing a quantitative analysis regarding the contents of WCl₂, WCl₄, WCl₆, and W-O-CI-based acid chloride as compound impurities based on the TG method, the contents were respectively 0 wt%, 0 wt%, 1 wt%, and 4 wt%, and the yield of WCl₅ was 19%. When the chloride of the reducing agent quickly becomes gasified as with this Example, while this is effective in reducing metal impurities other than the reducing agent, a large amount of WCl₆ will remain, and the yield will deteriorate considerably.

(Example 7)

This example is not in accordance with the claimed invention. WCl₆ having a purity of 4N and Ti having a purity of 5N as a reducing agent were uniformly mixed with a mortar in a nitrogen atmosphere to achieve a total mass of 1 kg at a molar ratio of 6:1. Next, the obtained mixture was placed in a vacuum vessel and heated at 130°C for 24 hours to reduce WCl₆ while maintaining the ambient pressure in the vessel to be an atmospheric pressure (approximately 0.1 MPa). In this Example, while the chloride of the reducing agent was subject to the condition in which the liquid phase state is maintained during the reduction operation, the amount of the reducing agent has decreased. Subsequently, the reduced product obtained with the foregoing reduction operation was subject to reduced-pressure distillation, and the thus obtained reduced-pressure distilled product was additionally subject to sublimation purification. The conditions of reduced-pressure distillation and sublimation purification were the same as Example 1. Subsequently, the obtained WCl₅ was recovered in a nitrogen atmosphere and sealed in an ampule.
Results of performing trace element analysis to the recovered WCl₅ are shown in Table 1. As impurities excluding Ti that was used as the reducing agent, K and Mo were detected in excess of the detection lower limit, the total content thereof was slightly 2.5 wtppm. Nevertheless, in this Example in which the amount of the reducing agent is smaller than Example 2, residue of Ti in an amount of 0.2 wtppm was acknowledged. Furthermore, as a result of performing a quantitative analysis regarding the contents of WCl₂, WCl₄, WCl₆, and W-O-CI-based acid chloride as compound impurities based on the TG method, the contents were respectively 0 wt%, 0 wt%, 30 wt%, and 8 wt%, and the yield of WCl₅ was 8%. When the amount of the reducing agent is small, while this is effective in reducing metal impurities other than the reducing agent, a large amount of WCl₆ will remain, and the yield will deteriorate considerably.

(Comparative Example 1)

In the modes which respectively apply bismuth (Bi), mercury (Hg), aluminum (Al), and phosphorus (P) as the reducing agent, thermodynamic simulation was performed and examined. Nevertheless, it was discovered that, with these elements, in reality it is impossible to stably maintain a liquid phase state because the chloride is directly sublimated from a solid phase and becomes a gas phase. Because it became evident that it is difficult to reduce WCl₆ in a high purity and at a high yield based on the foregoing result, these elements were only examined regarding their feasibility as a reducing agent.

(Comparative Example 2)

WCl₆ having a purity of 4N was placed in a vacuum vessel to achieve a total mass of 1 kg, the atmosphere in the vessel was caused to be a hydrogen flow based on the reduction method of Non-Patent Document 1, and WCl₆ was heated and reduced at 350°C for 24 hours. Subsequently, the reduced product obtained with the foregoing reduction operation was subject to reduced-pressure distillation, and the thus obtained reduced-pressure distilled product was additionally subject to sublimation purification. The conditions of reduced-pressure distillation and sublimation purification were the same as Example 1. Subsequently, the obtained WCl₅ was recovered in a nitrogen atmosphere and sealed in an ampule.
Results of performing trace element analysis to the recovered WCl₅ are shown in Table 1. As impurities, Fe, K and Mo were detected in excess of the detection lower limit, and the total content thereof was 20 wtppm, and exceeded 10 wtppm. Furthermore, as a result of performing a quantitative analysis regarding the contents of WCl₂, WCl₄, WCl₆, and W-O-CI-based acid chloride as compound impurities based on the TG method, the contents were respectively 0 wt%, 0 wt%, 15 wt%, and 4 wt%, and the yield of WCl₅ was slightly 3%. The hydrogen reduction method known as a conventional technique ended in an unrealistic result in terms of actual practical application from the perspective of yield and industrial productivity.

(Comparative Example 3)

WCl₆ having a purity of 4N and Sb having a purity of 5N as a reducing agent were uniformly mixed with a mortar in a nitrogen atmosphere to achieve a total mass of 1 kg at a molar ratio of 3:1. Next, the obtained mixture was placed in a vacuum vessel and heated at 150°C for 24 hours to reduce WCl₆ while maintaining the ambient pressure in the vessel to be an atmospheric pressure (approximately 0.1 MPa). During this reduction operation based on heating, SbCl₃, which is chloride of Sb as the reducing agent, was subject to the condition of maintaining a liquid phase state. In this Example, the reduced product was directly recovered without undergoing reduced-pressure distillation and sublimation purification.
Results of performing trace element analysis to the recovered reduced product are shown in Table 1. As impurities excluding Sb that was used as the reducing agent, Na, Fe, K and Mo were detected in excess of the detection lower limit, and the total content thereof was 37.8 wtppm, and exceeded 10 wtppm. Moreover, residue of Sb used as the reducing agent in an amount of 29000 wtppm was acknowledged. Furthermore, in this Example, because reduced-pressure distillation and sublimation purification were not performed, various types of compounds other than the intended WCl₅ were contained in a large amount in the product. Moreover, because it was not possible to recover the sublimated/purified product, quantitative analysis based on the TG method was impossible. Accordingly, in this Example, it was not possible to ultimately obtain the intended WCl₅.

(Comparative Example 4)

WCl₆ having a purity of 4N and Sb having a purity of 5N as a reducing agent were uniformly mixed with a mortar in a nitrogen atmosphere to achieve a total mass of 1 kg at a molar ratio of 3:1. Next, the obtained mixture was placed in a vacuum vessel and heated at 150°C for 24 hours to reduce WCl₆ while maintaining the ambient pressure in the vessel to be an atmospheric pressure (approximately 0.1 MPa). During this reduction operation based on heating, SbCl₃, which is chloride of Sb as the reducing agent, was subject to the condition of maintaining a liquid phase state. Subsequently, the reduced product obtained with the foregoing reduction operation was subject to reduced-pressure distillation based on the same conditions as Example 1. In this Example, the obtained reduced-pressure distilled product was recovered without undergoing sublimation purification.
Results of performing trace element analysis to the recovered reduced-pressure distilled product are shown in Table 1. As impurities excluding Sb that was used as the reducing agent, Na, Fe, K and Mo were detected in excess of the detection lower limit, and the total content thereof exceeded 10 wtppm. Moreover, residue of Sb used as the reducing agent in an amount of 19000 wtppm was acknowledged. Furthermore, as a result of performing a quantitative analysis regarding the contents of WCl₂, WCl₄, WCl₆, and W-O-CI-based acid chloride as compound impurities based on the TG method, the contents were respectively 0 wt%, 0 wt%, 10 wt%, and 10 wt%, and the yield of WCl₅ was 34%. Since sublimation purification was not performed in this Example, the amount of the reducing agent and the amount of metal element impurities other than the reducing agent were great, and the yield of WCl₅ was also low.

(Comparative Example 5)

WCl₆ having a purity of 4N and Ti having a purity of 5N as a reducing agent were uniformly mixed with a mortar in a nitrogen atmosphere to achieve a total mass of 1 kg at a molar ratio of 4:1. Next, the obtained mixture was placed in a vacuum vessel and heated at 130°C for 24 hours to reduce WCl₆ while maintaining the ambient pressure in the vessel to be an atmospheric pressure (approximately 0.1 MPa). During this reduction operation based on heating, TiCl_4, which is chloride of Ti as the reducing agent, was subject to the condition of maintaining a liquid phase state. In this Example, the reduced product was directly recovered without undergoing reduced-pressure distillation and sublimation purification.
Results of performing trace element analysis to the recovered reduced product are shown in Table 1. As impurities excluding Ti that was used as the reducing agent, Na, Fe, K and Mo were detected in excess of the detection lower limit, and the total content thereof was 36.8 wtppm, and exceeded 10 wtppm. Moreover, residue of Ti used as the reducing agent in an amount of 31000 wtppm was acknowledged. Furthermore, in this Example, because reduced-pressure distillation and sublimation purification were not performed, various types of compounds other than the intended WCl₅ were contained in a large amount in the product. Moreover, because it was not possible to recover the sublimated/purified product, quantitative analysis based on the TG method was impossible. Accordingly, in this Example, it was not possible to ultimately obtain the intended WCl₅.

(Comparative Example 6)

WCl₆ having a purity of 4N and Ti having a purity of 5N as a reducing agent were uniformly mixed with a mortar in a nitrogen atmosphere to achieve a total mass of 1 kg at a molar ratio of 4:1. Next, the obtained mixture was placed in a vacuum vessel and heated at 130°C for 24 hours to reduce WCl₆ while maintaining the ambient pressure in the vessel to be an atmospheric pressure (approximately 0.1 MPa). During this reduction operation based on heating, TiCl_4, which is chloride of Ti as the reducing agent, was subject to the condition of maintaining a liquid phase state. Subsequently, the reduced product obtained with the foregoing reduction operation was subject to reduced-pressure distillation based on the same conditions as Example 1. In this Example, the obtained reduced-pressure distilled product was recovered without undergoing sublimation purification.
Results of performing trace element analysis to the recovered reduced-pressure distilled product are shown in Table 1. As impurities excluding Sb that was used as the reducing agent, Na, Fe, K and Mo were detected in excess of the detection lower limit, and the total content thereof was 24.6 wtppm, and exceeded 10 wtppm. Moreover, reside of Ti used as the reducing agent in an amount of 11000 wtppm was acknowledged. Furthermore, as a result of performing a quantitative analysis regarding the contents of WCl₂, WCl₄, WCl₆, and W-O-CI-based acid chloride as compound impurities based on the TG method, the contents were respectively 0 wt%, 0 wt%, 8 wt%, and 7 wt%, and the yield of WCl₅ was 58%. Since sublimation purification was not performed in this Example, the amount of the reducing agent and the amount of metal element impurities other than the reducing agent were great, and the yield was less than 60%.

INDUSTRIAL APPLICABILITY

According to the present invention, high purity tungsten pentachloride and tungsten pentachloride containing a moderate amount of a dopant element can be produced at a high yield and in an efficient manner. Since it is thereby possible to effectively supply tungsten pentachloride materials having a purity level required for use as electronic component materials of semiconductor devices and the like, high purity chemical synthetic catalysts, and compound raw materials etc, the present invention is expected to become a major contributor to the industrial field of semiconductor equipment, electronic materials, and organic synthetic chemistry and so on.

Claims

A method of producing tungsten pentachloride, comprising:
uniformly mixing one or more types of reducing agents selected from Sb, Ti, and As; and a tungsten hexachloride at a molar ratio of the reducing agent(s) to the tungsten hexachloride of 1.0:2.0 to 1.0:5.0 in an inert atmosphere to obtain a mixture;

heating and reducing the mixture for 1 to 100 hours in pressure and temperature ranges in which a chloride or chlorides of the reducing agent(s) become(s) a liquid phase, to obtain a reduced product;

heating the reduced product for 1 to 100 hours at 100 Pa or less and in a temperature range of 90 to 130°C, and performing reduced-pressure distillation thereto to obtain a reduced-pressure distilled product; and

heating and sublimating the reduced-pressure distilled product for 1 to 100 hours at 100 Pa or less and at a temperature range of 130 to 170°C, and performing sublimation purification at 70 to 120°C in an inert atmosphere of 100 Pa or less to precipitate tungsten pentachloride.
The production method of tungsten pentachloride according to claim 1, wherein a grain size of raw materials upon reduction is 200 µm or less.
The production method of tungsten pentachloride according to claim 1 or claim 2, wherein Ti is used as the reducing agent.
The production method of tungsten pentachloride according to any preceding claim, wherein the pressure and temperature ranges in which the chloride(s) of the reducing agent(s) become(s) a liquid phase are 0.1 to 2 MPa and 70 to 130°C, respectively.
The production method of tungsten pentachloride according to any preceding claim, wherein reduction is performed in a dry nitrogen flow atmosphere having a moisture content of 10 wtppm or less.
The production method of tungsten pentachloride according to any preceding claim, wherein a yield of tungsten pentachloride is 65% or higher.